Grim and methodical, writer-director Paul Haggis's "In the Valley of Elah" has a message-movie self-importance. It's one of the first Iraq-themed movies out of the gate, and it aims to be, if not the last word on the subject, then certainly one of the strongest.

Tommy Lee Jones plays Hank Deerfield – Vietnam vet, retired sergeant, and Tennessee truck hauler – who gets a call from Fort Rudd in New Mexico that his son Mike (Jonathan Tucker) has just returned from Iraq and gone AWOL. Hank drives to the base, leaving behind his distraught wife (Susan Sarandon, in a tiny part), and discovers when he gets there that the commanders and Mike's platoon buddies are either clueless or uncooperative.

When it is soon discovered that Mike was brutally murdered and dismembered in a remote area bordering Army and local jurisdictions, the official uncooperativeness continues, with only a local civilian cop, Detective Emily Sanders (Charlize Theron), willing to pursue the leads that Hank for the most part comes up with on his own.

At first "In the Valley of Elah" resembles nothing so much as a detective story with a political backdrop. Hank pieces the information together while maintaining an almost inhuman stoicism. He's the strong, silent type familiar from many a Western, but here his near-silence isn't mythic, it's painful to behold. Everything about Hank is painful. From the moment he hears the news of his son, his face crumples into a baggy mask of woe. Jones is so good at portraying hard-driven, nuggety men that his vulnerability here is doubly wrenching.

But, as powerful as Jones can be, Haggis never allows Hank a dimension beyond stoicism, as if we might not respect him if we saw him cry. As the movie moves through its murder mystery mode and begins racking up political points, Hank becomes a stand-in for all those Americans bewildered and beleaguered by the war. He becomes a Symbol.

Haggis, whose "Crash" was among the most overpraised Hollywood movies of recent years, scores his points one at a time. In an early scene, a TV set playing in the background has President Bush declaring that "Freedom is on the march." This TV motif, which recurs, drips with irony. Later on, one of Mike's platoon buddies says that the only way to exit Iraq is to nuke it. America, we are told, should not send heroes to places like Iraq.

Haggis maintains a superficial evenhandedness but in fact the movie, which is loosely based on a real incident, is an indictment of the Iraq war in all its ramifications. Haggis is saying that an unjust war produces psychological horrors far beyond those seen in just wars. He is saying that the all-American heroes fighting over there are rendered soulless by the meaningless of the bloodshed.

But is it really true that wars such as Iraq and Vietnam, because of their unpopularity, produced greater psychiatric distress among their combatants than, say, World War I or World War II? The notion that good wars are less harrowing for soldiers than bad ones is sentimental – and politically loaded. But even if Haggis is correct about this, it's a pretty tenuous basis for an indictment. There will always be vets who are rendered psychotic by the hazards of war – any war. The vets in this movie are made to shoulder the blame for Iraq instead of the lawmakers who sent them into battle. Haggis wields a big bazooka but his aim is low.

Nevertheless, "In the Valley of Elah" – the title refers to the battleground where Goliath and David fought – held me despite my many qualms. That's because the subject matter is innately powerful and resists Haggis's pigeonholing. He's latched onto something that's bigger than himself. Grade: B–

• Rated R for violent and disturbing content, language and some sexuality/nudity.